JP2812427B2 - Cesium lithium borate crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cesium lithium borate crystal and a composition substitution crystal thereof. More specifically, the present invention relates to a cesium-lithium-borate crystal and its composition useful as a nonlinear optical crystal for wavelength conversion of a laser oscillation device or an optical parametric oscillation device used for ultraviolet lithography, laser micromachining, laser fusion, and the like. The present invention relates to a substituted crystal, a method for producing the same, and an optical device using the same.

[0002]

2. Description of the Related Art Conventionally, in a laser oscillator used for ultraviolet lithography, laser fine processing, laser fusion, and the like, it has been necessary to efficiently obtain stable ultraviolet light. As one method, attention has been paid to a method of efficiently converting the wavelength of a light source using a nonlinear optical crystal to efficiently obtain ultraviolet light.

For example, in a pulse YAG laser oscillation device as one of the laser oscillation devices, a non-linear optical crystal is used to convert the wavelength of a light source, and a pulse YA is used.
Third harmonic of G laser (wavelength 355 nm), or
A fourth harmonic (wavelength 266 nm) is generated. For the nonlinear optical crystal for wavelength conversion, which is indispensable for generating such ultraviolet light, many ingenuity have been devised so far, for example, beta barium metaborate (β-BaB ₂ O ₄ ) And lithium triborate (LiB ₃ O ₅ ), cesium triborate (CsB
Borate (borate) crystals such as ₃ O ₅ ) are known. Such a nonlinear optical crystal for wavelength conversion for generating ultraviolet light transmits light having a wavelength of 200 nm or less and has a high nonlinear optical constant.

[0004] However, such a non-linear for wavelength conversion
Β-BaB, one of the optical crystals _TwoO_FourIs its manufacture
In the process, phase transition is likely to occur during melt growth.
Crystal growth is very difficult, and the angle tolerance is narrow.
Therefore, versatility was very poor. Again
LiB, one of the nonlinear optical crystals for wavelength conversion,_ThreeO
₆And CsB_ThreeO₆In the manufacturing process
The growth time has become very long due to the growth of
In addition, phase matching can be achieved only for light having a wavelength around 555 nm.
For example, 3 obtained with an Nd-YAG laser
Can be used for generation of double harmonics (wavelength 355nm)
Despite the occurrence of the fourth harmonic (wavelength 266 nm)
Had the drawback that it could not be used.

The present invention has been made in order to solve the above-mentioned drawbacks of the prior art, and is capable of transmitting light having a shorter wavelength and converting the wavelength, and has a high conversion efficiency. Provided is a cesium-lithium-borate crystal, which is a high-performance nonlinear optical crystal for wavelength conversion having a wide allowable temperature range and a wide allowable angle range, and a composition substitution crystal thereof, and a method for producing the crystal and its use It also aims to provide a law.

[0006]

According to the present invention, there is provided a cesium lithium borate crystal having a chemical composition represented by CsLiB ₆ O ₁₀ in order to solve the above-mentioned problems. Further, the present invention provides a composition substitution product of the above crystal,
The chemical composition is

[0007]

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(M is at least 1 other than Cs and Li
0 ≦ x ≦ 1, 0 ≦ y ≦ 1
Wherein x and y are not 0 or 1 at the same time) or a crystal represented by the following formula:

[0009]

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[0010] The present invention also provides a crystal represented by the formula (L represents at least one kind of alkaline earth metal element and 0 <z <1). The present invention provides a method for producing the crystal by heating and melting a raw material mixture of each element, a method for producing the crystal grown by a melt (melting) method using a seeding method by a top seed kilopros method, and a flux method. The present invention also provides a method for producing the crystal grown by the method described above.

Further, the present invention also provides a harmonic converter and an optical parametric oscillator having the above-mentioned cesium-lithium-borate crystal or its composition-substituted crystal as optical means.

[0012]

The inventor of the present invention has developed beta-barium metaborate (β-BaB ₂ O) which is generally used as a conventional nonlinear optical crystal for wavelength conversion for generating ultraviolet light.
₄ ) Note that borate (borate) crystals such as lithium triborate (LiB ₃ O ₅ ) and cesium triborate (CsB ₃ O ₅ ) are generally borate crystals containing a single metal. However, they have found that by including a plurality of types of metal ions, a high-performance borate crystal, which has not been known, can be realized.

That is, the inventor of the present invention makes several kinds of borate crystals containing two or more kinds of metal ions such as alkali metals and alkaline earth metals, and irradiates these borate crystals with an Nd-YAG laser (wavelength 1064 nm). Then, an experiment for generating a second harmonic (wavelength 532 nm) was performed.
In these numerous experimental tests, we searched for the best metal combinations.

As a result, it has been found that a very strong second harmonic is generated particularly from a borate crystal containing both Cs and Li, and the cesium-lithium borate crystal of the present invention and a crystal as a composition substitute thereof are obtained. A completely new crystal was completed. In the production of the crystal of the present invention, an appropriate raw material mixture such as cesium carbonate (Cs ₂ CO ₃ ), lithium carbonate (Li ₂ CO ₃ ) and boron oxide (B ₂ O ₃ ) is heated and melted as an initial raw material to thereby obtain a predetermined material. To produce crystals. The reaction formula at this time is, for example,

[0015]

Embedded image

Can be expressed as follows. Cs, Li
The cesium-lithium-borate crystal substituted by an alkali metal element (M) other than

[0017]

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As described above, those using any alkali metal element other than Cs and Li are considered. For example, when the alkali metal element (M) is Na (sodium), the composition of about 0 <x ≦ 0.01 is expressed as K
In the case of (potassium), the composition of about 0 <x ≦ 0.1
In the case of b (rubidium), a composition satisfying about 0 <x ≦ 1 is exemplified as a suitable range from the viewpoints of production, physical properties, and the like. Of course, a plurality of alkali metal elements may be added.

By adding these alkali metal ions, the refractive index of the crystal can be changed, so that not only the phase matching angle, the angle tolerance, the temperature tolerance, etc. can be improved, but also the structural change of the crystal at the same time. Gives more stable crystals that are hardly cracked and do not become cloudy. Also,

[0020]

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In the case of (1), alkaline earth metal (L) ions of Ba, Sr, Ca and Mg are added. As in the case of using only alkali metal, it is possible to change the refractive index of the crystal by adding these alkaline earth metal ions, thereby improving the phase matching angle, angle tolerance, temperature tolerance, etc. By giving the structural change of, a more stable crystal that is hard to crack can be obtained.

According to the present invention, the above crystal can be used for harmonic conversion and optical parametric oscillation (OPO). That is, the present invention also realizes an optical device including the above crystal. Hereinafter, the present invention will be described in more detail with reference to examples. Of course, the present invention is not limited by the following examples.

[0023]

EXAMPLES Example 1 Cs ₂ CO ₃ , Li ₂ CO ₃ , and B ₂ O ₃ were used as raw materials, and they were mixed at a molar ratio of 1: 1: 6 and melted by heating. Crystals were produced. At this time, the melting point of the crystal was 850 ° C.

A melt (melting) method is used as a method for growing crystals, a top seed method is used for seeding, and a growth period of about 2 weeks is 30 × 25 × 25 mm by a temperature drop method.
Transparent crystals of the size The chemical structural formula of the obtained crystal was confirmed to be CsLiB ₆ O ₁₀ from the results of composition analysis such as ICP emission spectroscopy and ICP mass spectrometry. As a result of measuring the melting point using differential thermal analysis, the melting point of the cesium lithium borate crystal was 850.1 ° C.
Met. In addition, a tetragonal crystal (space group I4
2d). In addition, this cesium
The lithium borate crystal was transparent to light in the visible region, and transmitted light up to a wavelength of 178 nm.

When the effective second-order nonlinear optical constant was determined by using the powder method, d _eff = 4d _KDF . Further, this 30 × 25 × 25 mm cesium lithium borate crystal was cut out at a phase matching angle, and the polished crystal was irradiated with a neodymium YAG laser beam having a wavelength of 1.06 μm, resulting in a second harmonic. It was confirmed that ultraviolet light having a certain wavelength of 0.53 μm was efficiently obtained.

The rotation pulling method (rotation rate 10 rpm)
m, lifting rate 0.5 mm / h), 10φ × 20
mm cesium lithium borate crystals were grown.
It was confirmed that it was the same as above. Example 2 Cesium carbonate (Cs ₂ CO ₃ ), lithium carbonate (Li ₂
Cesium lithium borate crystal (CsLiB ₆ O ₁₀ ) having a stoichiometric composition is produced by heating and melting a mixture of CO ₃ ) and boron oxide (B ₂ O ₃ ),
The cesium-lithium-borate crystal was grown in a five-layer controlled growth furnace by a seeding method using a top seed kilopross method. FIG. 1 shows a structural diagram of a five-layer controlled growth furnace used for crystal growth. This five-layer controlled growth furnace has a structure in which a cylindrical platinum crucible is installed in a vertical five-stage resistance heating furnace capable of keeping the furnace temperature uniform. In this cylindrical platinum crucible, a platinum wire is used as a nucleus for growing a crystal, a seed crystal of cesium lithium borate having a stoichiometric composition is attached to the platinum wire, and the seed crystal is rotated at a speed of 15 rotations per minute. , And the crystal was grown while reversing the direction of rotation every three minutes. At this time, the temperature in the platinum crucible is kept at 848 ° C., which is the melting point of the crystal. Thereby, 2.9cm × 2.0c in about 4 days
A transparent and high-quality cesium-lithium-borate crystal having a size of mx 2.2 cm and free from cracks could be grown. This is a very short period of growth compared to the conventional growth of a borate nonlinear optical crystal for wavelength conversion. Therefore,
According to the method for growing a cesium lithium borate crystal of the present invention, a cesium lithium borate crystal can be easily grown in a very short time.

The cesium-lithium-borate crystal is represented by R
As a result of a crystal structure analysis using an igaku AFC5R X-ray diffractometer, the crystal was a tetragonal crystal belonging to the space group I42d symmetry group, and the lattice constant of the crystal was a = 10.494 ° and c =
8.939 °, the calculated density was found to be 2.461 g / cm ³ . FIG. 2 shows a three-dimensional structure of the cesium-lithium-borate crystal, in which cesium atoms are located in a channel of a borate ring composed of boron and oxygen. This is because the non-linear optical crystal LiB, which is generally used conventionally, is
It became clear that the structure was completely different from that of ₃ O ₅ or CsB ₃ O ₅ (both orthorhombic).

The cesium-lithium-borate crystal was measured for its transmission spectrum and found that the wavelength was 18
It was transparent with light from 0 nm to 275 nm. FIG. 3 shows a transmission spectrum in a short wavelength region. As apparent from FIG. 3, the absorption edge is at 180 nm, which is about 9 nm shorter than the conventional BBO (189 nm).

The refractive index of the cesium lithium borate crystal was measured by the prism method in the wavelength range of 240 nm to 1064 nm. FIG. 4 shows the refractive index dispersion curve. In FIG. 4, no denotes a refractive index for an ordinary ray, and ne denotes a refractive index for an extraordinary ray. A refractive index approximation (Selmeier equation) obtained from the refractive index dispersion curve is as follows.

[0030]

(Equation 1)

Example 3 The relationship between the mixing ratio of B ₂ O ₃ and the temperature at the time of producing the cesium-lithium-borate crystal was measured. While maintaining the mixture ratio of Cs ₂ CO ₃ and Li ₂ CO ₃ as the initial raw materials at 1: 1, the mixture ratio of B ₂ O ₃ is 66.7% or more.
The melting point of the crystal was determined by subjecting the mixture to a sintered powder of the obtained mixture by a differential thermal analyzer with the temperature varied within the range of 83.3%. FIG. 5 is a phase diagram showing the relationship between the mixing ratio of B ₂ O ₃ and the temperature at this time. In FIG. 5, the mixing ratio is 1:
Cs ₂ CO ₃ and Li ₂ CO ₃ are Cs ₂ O + Li ₂
It is indicated as O. As is clear from FIG. 5, CsLiB ₆ O ₁₀ crystals could be obtained stably when the mixing ratio of B ₂ O ₃ was in the range of 66.7% to 81.8%. When the mixing ratio of B ₂ O ₃ is 66.7% or less, CsLiB
CBO was simultaneously precipitated in addition to the ₆ O ₁₀ crystal, and 8
In the range of 1.8% ~83.3% CsLiB ₆ O ₁₀ causes unknown crystal other than the crystal is simultaneous precipitation, crystal production has become unstable. Therefore, in the production of the cesium lithium borate crystal, it was found that it is preferable to use B ₂ O ₃ as the initial raw material in a mixing ratio of 66.7% to 81.8%. In addition, the melting point of the CsLiB ₆ O ₁₀ crystal that was stably manufactured was 848 ° C., and it was found that harmonic melting was performed at this temperature.

As described above, the cesium lithium borate crystal has a melting point of 848 ° C., which is lower than the melting point of the conventional nonlinear optical crystal, and has a harmonic melting composition. In comparison with β-BaB ₂ O ₄ , which tends to cause a phase transition, and LiB ₃ O ₅ , which has a very long growth time due to flux growth, it is easy to grow a high-quality crystal having a constant composition in a short period of time. It is possible to adopt the seeding method by the top seed kilopros method or the flux method. Example 4 Cesium carbonate (Cs ₂ CO ₃ ), lithium carbonate (Li ₂
Co ₃ ) and boron oxide (B ₂ O ₃ ) in a ratio of 1: 1: 5.
5 (B ₂ O ₃ 73.3%) to produce a cesium-lithium-borate crystal by 12kg heated and melted in a mixing ratio of the cesium-lithium-borate crystal 5
It grows large by the flux method in the layer control growth furnace. The flux method is suitable for growing large crystals because it is necessary to increase the temperature drop width. Platinum crucible is 20cm in diameter and 20cm in height to grow large crystals
Was used. At this time, the growth saturation temperature is 845.
° C. Growth temperature from 845 ° C to 843.5 ° C
The crystal was grown by lowering the temperature by about 0.1 ° C. per day. Thereby, 13cm x 12cm x in about 21 days
A large transparent single crystal having a size of 10 cm and a weight of about 1.6 kg could be grown. In this crystal growth, the conventional L
Hopper Gr observed in iB ₃ O ₅ crystal growth
No unstable growth such as owth was observed, and the growth was very stable. Example 5 In a Nd: YAG laser, Nd: YA was obtained by using the cesium-lithium-borate crystal (CsLiB ₆ O ₁₀ ) of the present invention as a nonlinear optical crystal for wavelength conversion.
Second harmonic (SH) of G laser (wavelength 1064 nm)
G: wavelength 532 nm).

FIG. 6 shows the relationship between the phase matching angle θ of the crystal capable of generating the second harmonic (SHG) and the wavelength of the incident laser. In FIG. 6, the dotted line is Type-
The solid line shows the calculated value by the Cell Meyer equation of the type I SHG, the solid line shows the calculated value by the Cell Meyer equation of the Type-II type SHG, and the black dots show the actually measured values. SHG
The wavelength limit is 477 nm for Type-I type and Type-I type.
It is 640 nm for type II. As is apparent from FIG. 6, for example, the Type-I type SHG incident angle of the Nd: YAG laser beam having a wavelength of 1064 nm is calculated as 29.
6 ° C., the measured value is about 30 ° C., and the wavelength 532 n
Type-I type SHG of m Nd: YAG laser light
The incident angle is 62.5 ° C. in the calculation and 62 ° C. in the actually measured value.

FIG. 7 shows the relationship between walk-off angle and wavelength for Type-I type SHG obtained by calculation from the Cellmeier equation. In FIG. 7, the solid line represents the CLBO of the present invention, and the dotted line represents the conventional BBO.
Is shown. Table 1 shows that the incident wavelength is 1064 nm,
CLBO of the invention at 532 nm and conventional BBO
Phase matching angle θ for Type-I type SHG, effective nonlinear optical constant d _eff , allowable angle Δθ · L, allowable wavelength Δ
It shows calculated values of λ · L, allowable temperature ΔT · L, walk-off angle, and laser damage threshold. The refractive index for BBO required to calculate these values is described in J. Appl. Phys, vol. 62, D. Eimerl, L. Davis,
By S. Velsko, EK Graham, A. Zalkin (1987
Year) p. Reference values shown in 1968 were used.

The effective nonlinear optical constant d _eff is KH ₂ P
Obtained by comparison with SHG of O ₄ (KDP) crystal. CLBO has exactly the same crystal structure as KDP, the second-order nonlinear optical constant is represented by d ₃₆ , and the relationship with d _eff is d d
_eff = −d ₃₆ sin θ sin 2φ D _eff was determined by using this equation. Reference value d ₃₆ of the KDP was used 0.435pm / V.

The allowable angle Δθ · L and the allowable wavelength Δλ · L were calculated from the Selmeier equation. Also, the temperature tolerance Δ
Since TL cannot be obtained from calculation, it was measured in the range of 20 ° C to 15 ° C.

[0037]

[Table 1]

As is apparent from Table 1, the CLBO of the present invention has a much larger angle tolerance and wavelength tolerance than the conventional BBO, despite having a much smaller effective nonlinear optical constant. It has a lower temperature tolerance and a smaller walk-off angle. Therefore,
The cesium lithium borate crystal of the present invention can perform wavelength conversion more effectively than a conventional nonlinear optical crystal. Example 6 In a Nd: YAG laser, the cesium
Nd: YAG laser (wavelength: 1064 nm) by using lithium borate crystal (CsLiB ₆ O ₁₀ )
(4HG: wavelength 266 nm) was generated. As incident light, second harmonic light (SHG) of a Q-switch laser having a pulse width of 8 nanoseconds was used, and the incident light was repeatedly irradiated at a beam diameter of 4 mm and 10 Hz. FIG.
It shows the relationship between the energy output of the incident light SHG and the energy output of 4HG, that is, the fourth harmonic generation characteristic. In FIG. 8, the solid line indicates the CLBO of the present invention.
, And the dotted line indicates BBO. Sample length is CLB
O is 9 mm and BBO is 7 mm. As is apparent from FIG. 8, as the energy of the incident light, SHG, increases, the energy of 4HG of BBO tends to saturate. However, the CLBO of the present invention is proportional to the square of the incident energy. It can be seen that in the high incident energy region where the light energy is large, a 4HG output with higher energy than BBO is obtained. Therefore, the cesium lithium borate crystal of the present invention can be used as a very excellent nonlinear optical crystal for wavelength conversion capable of generating high-power ultraviolet light. Example 7 In a Nd: YAG laser, the cesium
Nd: YAG laser (wavelength: 1064 nm) by using lithium borate crystal (CsLiB ₆ O ₁₀ )
(5HG: wavelength 213 nm).

FIG. 9 shows a frequency (ω ₁ + ω ₂ = ω ₃ ) at which a sum frequency can be generated for _two frequencies of light (ω ₁ , ω ₂ ) in the CLBO of the present invention from the Cellmeier equation.
Is the result of calculating. The horizontal axis is frequency ω ₁
Wavelength lambda ₁ of the light corresponding to, the vertical axis represents the wavelength lambda ₃ of the light corresponding to the wavelength lambda ₂ and the frequency omega ₃ of light corresponding to the frequency omega _2. In FIG. 9, a region indicated by oblique lines above the solid line is a region where sum frequency generation is possible. The dotted line indicates the wavelength λ ₃ obtained as a result of the sum frequency. For example,
Assuming that the fundamental wave (wavelength 1064 nm) of the Nd: YAG laser is ω, ω + 4ω = 5ω is possible. That is, the fifth harmonic can be generated by the sum frequency of the fundamental wave and the fourth harmonic. However, it is impossible to generate the fifth harmonic by the sum frequency of the second harmonic and the third harmonic.

In FIG. 9, the black points indicate the wavelength obtained by the sum frequency of ω + 4ω and the wavelength obtained by the sum frequency of 2ω + 3ω. Since only the black point indicating ω + 4ω exists in the shaded region, it can be seen that the fifth harmonic can be generated only by the sum frequency of ω + 4ω. Further, as is clear from the dotted line (wavelength λ ₃ ) in FIG. 9, by selecting appropriate wavelengths λ ₁ and λ ₂ ,
It can be seen that wavelengths of nm or less can be generated by the sum frequency.

FIG. 10 shows a photograph of a beam pattern at a frequency five times higher than that of the Nd: YAG laser generated by the CLBO of the present invention. FIG. 11 shows a crystal layout of the second harmonic, the fourth harmonic, and the fifth harmonic at that time. Table 2 shows the CL of the present invention.
It shows each frequency energy value of BO and conventional BBO. As is clear from Table 2, the conventional BBO
Is 20 mJ obtained by the method of the present invention.
It can be seen that 5ω obtained by LBO is a higher output of 35 mJ. Therefore, the cesium lithium borate crystal of the present invention has a higher output power than the conventional BBO.
It can generate a second harmonic and can be used as a very excellent nonlinear optical crystal for fifth harmonic generation.
The beam pattern obtained from FIG. 10 is also close to a circle, indicating that the wavelength can be changed over the entire beam. This is because CLBO has an angle tolerance Δθ compared to BBO.
-L is large.

[0042]

[Table 2]

Example 8 The output of an Ar laser at a wavelength of 488 nm was made a second harmonic by the cesium lithium borate crystal of the present invention. Table 1 shows that Type-I type SHG of CLBO of the present invention and conventional BBO at an incident wavelength of 488 nm.
, The effective nonlinear optical constant d _eff ,
Angle allowance Δθ · L, wavelength allowance Δλ · L, temperature allowance ΔT ·
The calculated values of L, walk-off angle, and laser damage threshold are shown. Each calculation method was calculated by the same method as described in Example 6. As is apparent from Table 1, the walk-off angle of CLBO is 0.98 degrees, which is almost close to the non-critical phase matching state. Therefore, the cesium-lithium borate crystal of the present invention is much more intense than the conventional BBO. It can be seen that the conversion efficiency is high. Embodiment 9 The cesium-lithium-borate crystal of the present invention was subjected to optical parametric oscillation (OP: optical parametric oscillati).
on).

Optical parametric oscillation (OPO) is a technique in which the non-linear polarization in a non-linear optical crystal is excited by laser light, so that the energy of the excitation light is split into signal light and idler light through the non-linear oscillation of polarized electrons. This is a wavelength conversion process, which can be tuned over a wide wavelength range, and is expected to be applied to a wide range. Cesium-lithium-borate crystal of the present invention has a relatively large effective nonlinear optical constant, the crystal length is taken long, because the power density of the excitation light is made large due to the high further pairs laser damage threshold, crystal for OPO It has excellent characteristics.

FIG. 12 shows that the wavelength of the excitation light is 213 nm,
T at 66 nm, 355 nm, and 532 nm
FIG. 4 is a phase matching tuning curve diagram showing a relationship between a wavelength of signal light generated in ype-I and a phase matching angle at that time. FIG. 13 is a phase matching tuning curve diagram showing the relationship between the wavelength of the signal light generated in Type-II and the phase matching angle at that time when the wavelength of the excitation light is 532 nm. As is apparent from FIGS. 12 and 13, it is understood that the cesium-lithium-borate crystal of the present invention exhibits excellent characteristics as an OPO crystal.

Particularly, in the case of the OPO excited by the fourth harmonic (wavelength 266 nm) of the Nd: YAG laser, 300 n
A variable wavelength laser light in the vicinity of m can be obtained, but this was impossible in the conventional BBO because the allowable angle Δθ · L was small and the walk-off was large. Example 10 In the same manner as in Example 2, Rs (rubidium) -substituted cesium-lithium-borate crystal Cs _1-x LiRb _x B ₆
The O ₁₀ was produced.

The obtained crystals were evaluated by the powder X-ray diffraction method. As a result, as shown in FIG. 14, the X-ray diffraction pattern of the sample (Rb, x = 0) to which Rb was not added was x =
By increasing the Rb amount in the order of 0.2, 0.5, and 0.7, the angular interval between the reflection on the (312) plane and the reflection on the (213) plane is gradually narrowed. This is Cs and R
This indicates that b enters the crystal at an arbitrary ratio. Rb Crystals optionally added is Ru tetragonal der the same crystal form as the CLBO not added Rb is, it can be seen that the lattice constant slide into change.

From this, it can be seen that the addition of Rb ions can be arbitrarily added, so that the refractive index of the crystal can be changed, and the phase matching angle, angle tolerance, temperature tolerance, etc. can be improved. did. Similarly, Rb
Was also produced with an addition amount (x) of 0.1 or less. It was confirmed that the stability of the crystal structure was better. Example 11 In Example 10, a crystal was produced by adding K and Na, respectively, instead of Rb. When the composition ratio (x) was K (potassium), it was 0.1 or less, and when Na (sodium), the composition ratio was 0.01 or less, and it was confirmed that good quality crystals could be obtained.

Also, a crystal in which K or Na coexists with Rb was produced. In this case, in the composition of Cs _1-x Li _1-y Rb _x (Na, K) _y B ₆ O ₁₀ , more stable crystals are obtained when 0 <x <1 and 0 <y <0.1. Was done. Example 12 In Example 10, a crystal was obtained in which an alkaline earth metal element was added instead of the alkali metal.

[0050] For example _{Cs 2 (1-z) Li} 2 Ba Z B 12 O 20
In the case of the composition, it was confirmed that a stable crystal was obtained at 0 <z ≦ 0.1.

[0051]

As described in detail, according to the present invention, a novel cesium lithium borate crystal can be provided. This crystal is capable of transmitting light of shorter wavelength and converting the wavelength, has a high conversion efficiency, and has a wide temperature tolerance and an angle tolerance.
It can be used as a high-performance wavelength conversion crystal. Furthermore, since the melting point is as low as 848 ° C., and since it is a harmonized molten composition, it is possible to easily grow a high-quality large crystal having a uniform composition in a short period of time by a melt method using a seeding method by a top seed kilopros method. Or the flux method.

[Brief description of the drawings]

FIG. 1 is a structural diagram showing a structural example of a five-layer control crystal growing furnace for growing a cesium lithium borate crystal according to one embodiment of the present invention.

FIG. 2 is a three-dimensional structural diagram showing the structure of the cesium lithium borate crystal of the present invention as viewed from the a-axis direction.

FIG. 3 is a diagram showing a transmission spectrum of a cesium lithium borate crystal of the present invention.

FIG. 4 is a diagram showing a refractive index dispersion curve of the cesium lithium borate crystal of the present invention.

FIG. 5 is a relationship diagram showing the relationship between the mixing ratio of boron oxide (B ₂ O ₃ ) and the temperature during the production of the cesium lithium borate crystal of the present invention.

FIG. 6 shows a relationship between an incident laser wavelength and a phase matching angle θ of a cesium-lithium-borate crystal Nd: YAG laser capable of generating a second harmonic (SHG) according to an embodiment of the present invention. FIG.

FIG. 7 is a diagram showing the relationship between the walk-off angle and the incident laser wavelength of a cesium lithium borate crystal according to an embodiment of the present invention in a Nd: YAG laser.

FIG. 8 is a diagram showing the fourth harmonic generation characteristics of a cesium lithium borate crystal according to one embodiment of the present invention.

FIG. 9 is a diagram showing a theoretical curve of a non-critical phase matching wavelength by generation of a sum frequency of a cesium-lithium borate crystal according to an embodiment of the present invention, and a resulting sum frequency wavelength.

FIG. 10 shows Nd: Y obtained by sum frequency generation of cesium lithium borate crystal according to one embodiment of the present invention.
It is a photograph instead of the drawing which showed the beam pattern of the 5th harmonic, the 2nd harmonic, and the 4th harmonic of the AG laser.

[11] that is obtained from the sum frequency generation of the cesium-lithium-borate crystal which is an embodiment of the present invention Nd: YA
5th harmonic of G laser, 2nd harmonic and 4th harmonic
FIG. 3 shows a crystal arrangement diagram of the occurrence .

FIG. 12 shows that the wavelength of the excitation light is 213 nm, 266 nm, and 3
Ty by cesium lithium borate crystal according to one embodiment of the present invention at 55 nm and 532 nm
It is a phase matching tuning curve figure of pe-IOPO.

FIG. 13 is a phase-matching tuning curve of a Type-II OPO using a cesium-lithium-borate crystal according to an embodiment of the present invention when the wavelength of the excitation light is 532 nm.

FIG. 14 is a diagram showing powder X-ray diffraction data of a crystal of Cs _1-x LiRb _x B ₆ O ₁₀ .

────────────────────────────────────────────────── ─── Continuation of the front page Application for Patent Law Article 30 (1) application is available. J. APP L. PHYS. VOL. 34 (1995) PP. L296-L298, PART2, NO. 3A, published in MARCH 1995 (58) Fields investigated (Int. Cl. ⁶ , DB name) C30B 29/22 G02F 1/35 G02F 1/37 H01S 3/18

Claims (9)

(57) [Claims] 1. A cesium lithium borate crystal having a chemical composition represented by CsLiB ₆ O ₁₀ . The chemical composition is represented by the following formula: Cs _1-x Li _1-y M _{x + y} B ₆ O ₁₀ (M represents at least one alkali metal element other than Cs and Li; 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and x
And y are not 0 or 1 at the same time). (3) a chemical composition represented by the following formula: Cs _{2 (1-z)} Li ₂ L _z B ₁₂ O ₂₀ (L is at least one kind of alkaline earth metal element;
0 <z <1) substituted cesium lithium borate crystal represented by the formula: 4. The method for producing a crystal according to claim 1, wherein the crystal is produced by heating and melting the raw material mixture of the constituent elements. 5. The method according to claim 4 , wherein the crystal is grown by a melting method. 6. The method according to claim 4 , wherein the crystal is grown by a flux method. 7. A harmonic converter comprising the crystal according to claim 1 as optical means. 8. The apparatus of claim 7 for generating 2, 4, or 5 harmonics of a laser. 9. An optical parametric oscillator comprising the crystal according to claim 1 as optical means.